I. Field of the Invention
The present invention relates generally to manhole and catch-basin structures used to both join sewer tubes and provide a cleaning or inspection shaft. More particularly, it relates to a caustic fluid blocking member that contains the caustic fluids and corrosive chemicals within the base of the manhole or catch-basin, thereby reducing exposure of the manhole and catch basin sidewalls to corrosive chemicals, thus extending the useful life of the structure.
II. Background of the Invention
Sanitary and storm sewer systems are typically comprised of a plurality of networked sewer pipelines. These pipelines are occasionally passed through or joined to one another at a manhole or catch-basin structure. These structures serve as a node for the sewer or drainage system, and also provide an access or inspection shaft. Devices for unclogging the sewer pipelines can be inserted into the sewer pipelines at the manhole structure location, and then guided through the pipes to remove obstructions proximate the manhole structure.
When a manhole or catch-basin is first constructed, it comprises a base with concentric sidewalls extending upward. Resting atop the concentric sides is a pre-cast cone. A cast iron support frame and cover or grate are placed onto the top of the cone. The base and cone of the manhole structures are typically comprised of mortared blocks or casted concrete and may weigh several tons. The lower portion of the base of the manhole is referred to as a canal-bed. Manholes and catch basins are buried beneath the earth's surface, and typically below roadways, at depths of 10 feet or more. Of course, the overall size of the base affects both the cost to manufacture the base and the cost to construct the manhole.
The base of the manhole or catch-basin structure may include one or more openings adapted to receive a tube, and a gasket or O-ring for sealing a tube to a corresponding socket of the base. This sealing arrangement inhibits sewage from leaking about the pipes into the phreatic water or ground water adjacent the canal-bed of the base. A variety of gasket seals are known which are adapted to provide a leak-proof seal between the base and the pipe. One such gasket seal is disclosed in U.S. Pat. No. 3,796,406 which is assigned to A-Lok Corporation of Trenton, N.J. This seal has a generally A-shape and is rooted by casting splayed legs into the upwardly extending concentric sides of the base about the opening formed therein. Another type of gasket is disclosed in U.S. Pat. No. 4,159,829, also assigned to A-Lok Corporation. This seal has a generally T-shaped anchoring flange and is also cast into the sides of the base about the opening. These gaskets can be difficult to orient during the casting of the base.
Once the manhole or catch basin is constructed, the fluids passing through tend to deteriorate the structure. For example, sewage and putrid water are very acidic, and may comprise hydrogen sulfide and sulfuric acid. Over time, exposure to sewage or putrid water can damage the concrete of the canal-bed, base, and cone. In catch basins, road salt also has the same affect on the canal-bed. This is due to the eventual breakdown of the concrete by the road salt, especially if the concrete is of poor quality. When repair or replacement of these manhole/catch basin structures is required, due to a deteriorated canal-bed, base or cone, the procedure is extremely expensive, time consuming, and difficult.
To meet the need of increasing the useful life of these structures and to protect the canal-bed, plastic liners or shells with integrally defined canals have been developed. One such canal-bed shell is disclosed in U.S. Pat. No. 4,483,643 to Guggemos. Guggemos describes building sewers or channels by assembling tubes and providing between the tubes canal-bed shells at least at those positions where cleaning shafts or wells or inspections shafts are to be provided. The canal-bed shell disclosed by Guggemos is either cast onto and upon a bed of concrete, or subsequently anchored thereto. A shaft is then erected above the canal-bed. Guggemos describes using a jointing compound or the like between the shaft and canal-bed to seal the canal-bed and avoid contamination of phreatic water. These jointing compounds may deteriorate, be misaligned or separate from the shaft and canal-bed liner, thereby increasing the risk of contamination to the phreatic water.
In the device disclosed by Guggemos, the depth of the canal is disclosed as being equal to or greater than the interior diameter of the sewer pipes coupled thereto. By requiring the height of the canal-bed shell to be at least greater than the internal diameter of the pipes or sewer tubes, a substantial amount of additional concrete or other material is required. This substantial amount of additional concrete increases the cost to manufacture, increases the overall weight of the canal-bed, and increase the cost of constructing the manhole. Hence, there is a need for a lined canal-bed or base of reduced weight that provides sufficient flow guidance within the canal-bed and seals completely with a corresponding pipe. Although the canal bed liner reduces the amount of corrosion to the base of the manhole structure, vapors from the sewage or putrid water, for example, may tend to erode the concrete sidewalls and cone. Hence, there is also a need to contain the corrosive vapors within the lower portion of the base of the manhole. The present invention meets these needs as well as other needs and overcomes these and other disadvantages of the prior art.